Board, packaging material and package as well as production and uses thereof

ABSTRACT

The invention relates to a process for producing board which comprises providing an aqueous suspension comprising cellulosic fibres; adding hydrotalcite to the suspension; dewatering the obtained suspension to provide a (i) single ply board. The invention further relates to board comprising one or more plies containing cellulosic fibres, wherein the board further comprises hydrotalcite distributed throughout at least one of said one or more plies.

This application claims priority based on U.S. Provisional PatentApplication No. 60/572,208, filed May 18, 2004.

FIELD OF THE INVENTION

The present invention generally relates to board containing cellulosicfibres and hydrotalcite as well as the production thereof; packagingmaterials and packages comprising the board and the production thereofas well as uses of the packaging materials for packaging of foodstuff,beverages, pharmaceuticals, cosmetics and tobacco.

BACKGROUND OF THE INVENTION

Packages are widely used throughout the world, for example to transportgoods and protect the contents of the packages. It has proven especiallydifficult to design packages for maintaining the original properties ofcontents, such as foodstuff, beverages, pharmaceuticals and cigarettes.The quality of the content may be reduced either by the content itselfchanging over time, or by quality-reducing substances being suppliedfrom or through the package. The content can be treated, e.g.pasteurised, as with milk, or dried, as with flour. Usually, thepackages are designed with several plies or layers which often are madeof different materials. Thus, each ply and each material has a specificquality and purpose in the package, such as preventing the transfer ofoxygen, water or water vapour to the content of the package.

Packaging materials are frequently used for packaging solid and liquidfoodstuffs and beverages, e.g. cereals, milk, juice, wine and water.Such packaging materials are usually made of board comprising severallayers or plies of cellulosic fibres, combined with one or more layersof plastic material in direct contact with the foodstuff or beverage.Despite the use of packages containing a combination of severalmaterials, the content may acquire an undesirable smell and/or tasteafter some time. The substances causing undesirable smell and taste areusually oxidation products formed during production and storage of theboard. Since the packaging blanks usually are shipped flat and openedwhen ready to be filled, the oxidation products may be transferred tothe plastic-coated inside of the packaging material.

It would be desirable to be able to provide board and board-containingpackaging materials and packages having less undesirable or unpleasantsmell and/or taste. It would also be desirable to be able to provideimproved processes for the production of such products.

SUMMARY OF THE INVENTION

The present invention is generally directed to a process for producingboard comprising

-   -   (i) providing an aqueous suspension comprising cellulosic        fibres;    -   (ii) adding hydrotalcite to the suspension;    -   (iii) dewatering the obtained suspension to provide a single ply        board.

The present invention is further generally directed to a process forproducing board which comprises

-   -   (i) providing an aqueous suspension comprising cellulosic        fibres;    -   (ii) adding hydrotalcite to the suspension;    -   (iii) dewatering the obtained suspension, to provide a ply        comprising cellulosic fibres and hydrotalcite; and    -   (iv) attaching said ply to one or more plies comprising        cellulosic fibres to provide a multi ply board comprising two or        more plies.

The present invention is also generally directed to board comprising oneor more plies containing cellulosic fibres, wherein the board furthercomprises hydrotalcite distributed throughout at least one of said oneor more plies.

The present invention is further generally directed to a method forproducing a packaging material which comprises

-   -   (i) providing board comprising one or more plies containing        cellulosic fibres and hydrotalcite; and    -   (ii) subjecting the board to one or more converting operations        selected from printing, varnishing, coating, laminating,        metallizing, die cutting, scoring, creasing, foil blocking,        embossing and folding.

The present invention is also generally directed to a packaging materialcomprising board which comprises one or more plies containing cellulosicfibres and hydrotalcite, wherein it further comprises one or moregrooves, creases or scores.

The invention is further generally directed to a procedure of making apackage comprising:

-   -   (i) providing a blank of packaging material comprising board        comprising one or more plies containing cellulosic fibres and        hydrotalcite;    -   (ii) filling the packaging blank with a solid or liquid content        to form an unsealed package; and    -   (iii) sealing the obtained package.

The present invention is also generally directed to a package comprisingboard containing cellulosic fibres and hydrotalcite, wherein it furthercomprises a solid or liquid content.

The invention is further directed to uses of the packaging materialcomprising board, which comprises one or more plies containingcellulosic fibres and hydrotalcite, for packaging of solid or liquidfoodstuffs, beverages, pharmaceuticals, cosmetics, chocolates,cigarettes or tobacco.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention it has been found that the problemscaused by undesirable and unpleasant smell and/or taste of board andpackaging materials and packages comprising board can be reduced byusing hydrotalcite in the production thereof as an additive to aqueouscellulosic suspensions. It has also been found that the presentinvention reduces the negative impact on board making processes by thepresence of disturbing and detrimental substances present in aqueouscellulosic suspensions, specifically problems caused by pitch, stickiesand anionic low molecular weight organics. It has further been foundthat the addition of hydrotalcite in conjunction with additives used formaking board also improves the performance of such additives as comparedto when hydrotalcite is not added. Examples of such additives for whichimproved performance can be observed include drainage and retentionaids, sizing agents, etc. Preferably, the hydrotalcite is used togetherwith one or more drainage and retention aids comprising at least onecationic polymer. Thus, the present invention makes it possible toobtain a reduction of undesirable or unpleasant smell and/or taste ofboard and packaging materials comprising board, improved drainage(dewatering) and retention as well as improved sizing in board makingprocesses, while simultaneously reducing the content of disturbing anddetrimental substances in the cellulosic suspension.

Hydrotalcite belongs to the group of materials referred to as clays. Theterm “hydrotalcite”, as used herein, refers to hydrotalcite andhydrotalcite-like clays including layered double hydroxide compounds,e.g. manasseite, pyroaurite, sjögrenite, stichtite, barbertonite,takovite, reevesite, desautelsite, motukoreaite, wermlandite,meixnerite, coalingite, chloro-magalumite, carrboydite, honessite,woodwardite, iowaite, hydrohonessite, mountkeithite, etc. Thehydrotalcite according to the invention can be derived from naturallyoccurring hydrotalcites, synthetic hydrotalcites and chemically and/orphysically modified naturally occurring and synthetic hydrotalcites.Naturally occurring hydrotalcites normally have an essentiallycrystalline structure.

However, synthetically obtained hydrotalcites may also contain amorphousmaterial having essentially the same chemical composition as thecrystalline structures. The amount of amorphous material present insynthetic hydrotalcite clays depends mainly on the reaction parametersused. The term “clay”, as used herein, refers to clays havingessentially crystalline structure and also to clays both containingcrystalline and amorphous structures.

Clays are characterised by a layered structure wherein atoms within thelayers (lamellae) are cross-linked by chemical bonds, while the atoms ofadjacent layers interact mainly by physical forces. The layers of theclay may be non-charged or charged depending on the type of atomspresent in the layers. If the layers are charged, then the space betweenthese layers, also designated as the interlayer space, contains ionswhich have the opposite charge with respect to the charge of the layers.The term “cationic clay”, as used herein, refers to clays havingpositively charged layers and anions present in the interlayer space.The term “anionic clay”, as used herein, refers to clays havingnegatively charged layers and cations present in the interlayer space.Usually the ions in the interlayer space are exchangeable. Preferably,the hydrotalcite of the invention is cationic, i.e. a cationic clay.

The hydrotalcite of the invention can virtually have any anion,optionally also water molecules, present in the interlayer space.Examples of common anions that can be present in the interlayer spaceinclude NO₃ ⁻, OH⁻, Cl⁻, Br⁻, I⁻, CO₃ ²⁻, SO₄ ²⁻, SIO₃ ²⁻, CrO₄ ²⁻, BO₃²⁻, MnO₄ ⁻, HGaO₃ ²⁻, HVO₄ ⁻, and ClO₄ ⁻, as well as pillaring orintercalating anions such as V₁₀O₂₈ ⁶⁻ and MO₇O₂₄ ⁶⁻, mono-carboxylateslike acetate, dicarboxylates such as oxalate, and alkyl sulphonates suchas lauryl sulphonate; usually hydroxide and carbonate. Naturallyoccurring hydrotalcites of the invention commonly have carbonate anionsin the interlayer space.

The layer or lamella of the hydrotalcite suitably comprises at least twodifferent metal atoms having different valences. Suitably, one metalatom is divalent and the other metal atom is suitably trivalent.However, the layer may also comprise more than two metal atoms. Thecharge of the layer is govemed by the ratio of metal atoms havingdifferent valences. For instance, a higher amount of trivalent metalswill render a layer having an increased density of the positive charge.Suitably, the hydrotalcite of the invention comprises layers containingdivalent and trivalent metals in a ratio so that the overall charge ofthe layers is cationic, and the interlayers comprise anions. Preferably,the layers essentially consist of divalent and trivalent metals in sucha ratio that the overall charge of the layers is cationic.

Synthetically produced and naturally occurring hydrotalcites accordingto the invention can be characterised by the general formula:[M_(m) ²⁺Mn³⁺(OH)_(2m+2n)]X_(n/z) ^(Z−) .bH₂O,wherein m and n, independently of each other, are integers having avalue such that m/n is in the range of from 1 to 10, preferably 1 to 6,more preferably 2 to 4 and most preferably values around 3; b is aninteger having a value in the range of from 0 to 10, suitably a valuefrom 2 to 6, and often a value about 4; X_(n/z) ^(Z−) is an anion wherez is an integer from 1 to 10, preferably from 1 to 6, suitable X_(n/z)^(Z−) including NO₃ ⁻, OH⁻, Cl⁻, Br⁻, I⁻, CO₃ ²⁻, SO₄ ²⁻, SiO₃ ²⁻, CrO₄²⁻, Bo₃ ²⁻, MnO₄ ²⁻, HGaO₃ ²⁻, HVO₄ ⁻, ClO₄ ⁻, pillaring andintercalating anions such as V₁₀O₂₈ ⁶⁻and MO₇O₂₄ ⁶⁻, mono-carboxylateslike acetate, dicarboxylates such as oxalate, and alkyl sulphonates suchas lauryl sulphonate; M²⁺ is a divalent metal atom, suitable divalentmetal atoms including Be, Mg, Cu, Ni, Co, Zn, Fe, Mn, Cd, and Ca,preferably Mg; M³⁺ is a trivalent metal atom, suitable trivalent metalatoms including Al, Ga, Ni, Co, Fe, Mn, Cr, V, Ti and In, preferably Al.

Preferably, the divalent metal is magnesium and the trivalent metal isaluminium, rendering the general formula:[Mg_(m) ²⁺Al_(n) ³⁺(OH)_(2m+2n]X) _(n/z) ^(Z−) .bH₂O.

Hydrotalcites according to the invention can be prepared by hydrothermaltreatment (solvo thermal) of a slurry containing an aluminium source anda magnesium source. Examples of suitable hydrotalcites of the inventionand methods for their preparation include those disclosed inInternational Patent Application Publication No. WO 01/12550, thedisclosure of which is hereby incorporated herein by reference.

In a preferred embodiment of the invention, the hydrotalcite has a 3R₂stacking. In another preferred embodiment of the invention, thehydrotalcite has a stacking other than the 3R₂ stacking, for example a3R, stacking. Differences between the hydrotalcite 3R₁ and 3R₂ stackingsare disclosed in International Patent Application Publication No. WO01/12550, the disclosure of which is incorporated herein by reference.

Preferably, the hydrotalcite is used according to the invention eitheras a slurry (suspension) or powder, which can be easily dispersed inwater. The suspension or powder of hydrotalcite may further also containother components such as, for example, dispersing and/or protectingagents, which can contribute to the overall effect of the hydrotalcite.Such agents can have non-ionic, anionic or cationic character. Examplesof suitable protective agents or colloids include water-solublecellulose derivatives, e.g. hydroxyethyl- and hydroxypropyl-,methylhydroxypropyl- and ethylhydroxyethyl-cellulose, methyl- andcarboxymethylcellulose, gelatine, starch, guar gum, xanthan gum,polyvinyl alcohol, etc. Examples of suitable dispersing agents includenon-ionic agents, e.g. ethoxylated fatty acids, fatty acids, alkylphenols or fatty acid amides, ethoxylated and non-ethoxylated glycerolesters, sorbitan esters of fatty acids, non-ionic surfactants, polyolsand/or their derivatives; anionic agents, e.g. as alkyl or alkylarylsulphates, sulphonates, ethersulphonates, polyacrylic acid; and cationicagent, e.g. esterquats obtained by reacting alkanolamines with mixturesof fatty acids and dicarboxylic acids, optionally alkoxylating theresulting esters and quatemising the products, quatemised fatty acidamides, betaines, dimethyl dialkyl or dialkylaryl ammonium salts, andcationic gemini dispersing agents.

According to the present invention, board is produced by a process whichcomprises adding hydrotalcite to an aqueous cellulosic suspension andthen dewatering the obtained suspension to form the board. In apreferred embodiment of the invention, the process produces a single plyboard comprising hydrotalcite which preferably is distributed throughoutthe board, more preferably substantially uniformly distributedthroughout the board. Single ply board contains just one ply or layercomprising cellulosic fibres.

In another preferred embodiment of the invention, the process produces amulti ply board comprising two or more plies or layers containingcellulosic fibres wherein at least one of said two or more plies orlayers comprises hydrotalcite. Preferably, the hydrotalcite isdistributed throughout at least one of said two or more plies, morepreferably substantially uniformly distributed throughout at least oneof said two or more plies, most preferably in at least one of the outerplies. Multi ply board according to the invention can be produced byforming at least one ply comprising cellulosic fibres and hydrotalciteand attaching said at least one ply to one or more plies comprisingcellulosic fibres to form the multi ply board. For example, multi plyboard can be produced by forming the individual plies or layersseparately in one or several web-forming units and then couching themtogether in the wet state. Examples of suitable grades of multi plyboard of the invention include those comprising from three to sevenplies or layers comprising cellulosic fibres and at least one of saidplies or layers comprising hydrotalcite.

In the process of the invention, the board, e.g. single and multi plyboard grades, can be subjected to further process steps. Examples ofsuitable process steps include coating, e.g. starch coating and pigmentcoating, printing and cutting. Accordingly, examples of suitable boardsof the invention include coated board, e.g. starch and/or pigmentcoated, and printed board.

The hydrotalcite can be added at any point in the board productionprocess starting from the point where wood chips are disintegrated up tothe point in the process where dewatering of the cellulosic suspensiontakes place.

According to a preferred embodiment of the invention, the hydrotalciteis added to a cellulosic suspension of a pulp making process. Thehydrotalcite can be added prior to or after the pulping process whichcan be kraft, mechanical, thermo-mechanical, chemomechanical,chemo-thermo-mechanical pulping processes. The hydrotalcite can be addedjust before the pulping process or directly to the pulping process, suchas to the digester. However, it is preferred that the hydrotalcite isadded to the cellulosic suspension subsequent to chemical digestion suchas after the brown stock washer, or after refining of (chemo-)mechanicalpulp. Usually, the cellulosic pulp is bleached in a multi stagebleaching process comprising different bleaching stages and thehydrotalcite can be added to any bleaching sequence. Examples ofsuitable bleaching stages include chlorine bleaching stages, e.g.elementary chlorine and chlorine dioxide bleaching stages, non-chlorinebleaching stages, e.g. peroxide stages like ozone, hydrogen peroxide andperacetic acid, and combinations of chlorine and non-chlorine bleachingand oxidizing stages, optionally in combination with reducing stageslike treatment with dithionite. The hydrotalcite can be added to thecellulosic suspension directly to a bleaching stage, preferably to themixer prior to the bleaching tower, at any point between the bleachingand washing stages, and also to a washing stage where the hydrotalcitemay be partly removed, e.g. in the displacement section. Preferably,when adding the hydrotalcite to a cellulosic suspension of a pulp makingprocess, the pulp obtained is subsequently used in a board makingprocess.

According to another preferred embodiment of the invention, thehydrotalcite is added to a cellulosic suspension of a board makingprocess. The hydrotalcite can be added to the cellulosic suspension atany point of the board making process such as to the thick stock, thinstock, or to the white water before it is recycled, e.g. prior to thethin stock feed box. Preferably, the hydrotalcite is added to the thickstock. The hydrotalcite can also be added at more than one point of thepulp and/or board making processes. For instance, in integrated pulp andboard mills, the hydrotalcite can be added in the process for pulpproduction, and optionally also in the process for board production, andone or more drainage and retention aids can be added in the process forboard production. Such processes can include dewatering the cellulosicsuspension containing hydrotalcite, diluting the suspension obtained,adding to the diluted suspension one or more drainage and retention aidsand dewatering the suspension containing the drainage and retentionaids.

The term “board, as used herein, refers to board comprising cellulosicfibres including solid board, e.g. solid bleached sulphate board (SBS)and solid unbleached sulphate board (SUS); paper board, carton board,e.g. folding boxboard (FBB), folding carton board, liquid packagingboard (LPB), including gable-top, aseptic, brick and non-asepticpackaging boards; white lined chipboard (WLC), unbleached kraftboard,grey chipboard and recycled board; liner board and container board,including white sulphate kraftliner, fully bleached kraftliner,testliner, white sulphate testliner, unbleached kraftliner, unbleachedtestliner and recycled liner; fluting and corrugated fluting.Preferably, the board has a grammage of at least 130 g/m², morepreferably in the range of from 140 to 600 g/m² and most preferably from150 to 450 g/m². Preferably, the board has a bulk density of 120 to 1200kg/m³, more preferably from 150 to 800 kg/m³ and most preferably from200 to 600 kg/m³. The process can be used in the production of boardfrom different types of aqueous suspensions comprising cellulosicfibres, or aqueous cellulosic suspensions. Preferably, the suspensioncontains at least 25% by weight and more preferably at least 50% byweight of such fibres, based on a dry substance. The cellulosic fibrescan be based on bleached and unbleached pulps, they can be based onvirgin and/or recycled fibres, and the suspension can be based on fibresfrom chemical pulp such as sulphate, sulphite and organosolve pulps,mechanical pulp such as thermo-mechanical pulp (TMP),chemo-thermo-mechanical pulp (CTMP), refiner pulp and ground wood pulp,from both hardwood and softwood, and can also be based on recycledfibres, optionally from de-inked pulps (DIP), and mixtures thereof. Inmulti ply board grades the plies can be made of different types of pulp.Examples of suitable multi ply combinations with bleached cellulosicfibre include bleached chemical pulp top/DIP, CTMP or mechanical pulpmiddle/bleached chemical pulp back; and bleached chemical pulp top/DIP,CTMP or mechanical pulp middle/mechanical pulp back; the top sideoptionally being coated and the back side optionally being coated.

The cellulosic suspension can also contain mineral fillers ofconventional types such as, for example, kaolin, china clay, titaniumdioxide, gypsum, talc and natural and synthetic calcium carbonates suchas chalk, ground marble and precipitated calcium carbonate.

Preferably, the hydrotalcite is added to the cellulosic suspension in anamount of from about 0.01% by weight to about 10% by weight, morepreferably from about 0.05% by weight up to about 5% by weight,calculated as dry hydrotalcite on a dry cellulosic suspension.

In the process of the invention the hydrotalcite is preferably used inconjunction with one or more additional additives by addition to theaqueous cellulosic suspension prior to dewatering. Examples of suitableadditional additives include drainage and retention aids, cationiccoagulants, sizing agents like rosin-based sizing agents andcellulose-reactive sizing agents, e.g. ketene dimers and succinicanhydrides, dry strength agents, wet strength agents like polymersformed by reaction of polyamines or polyamideamine with epichlorohydrin,optical brightening agents, dyes, etc.

Examples of suitable drainage and retention aids include organicpolymers, which can be selected from anionic, amphoteric, non-ionic andcationic polymers, siliceous materials, and mixtures thereof. The use ofsiliceous materials and organic polymers as drainage and retention aids,or as flocculating agents, is well known in the art. The term “drainageand retention aid”, as used herein, refers to a component (agent,additive) which, when being added to an aqueous cellulosic suspension,give better drainage and/or retention than is obtained when not addingsaid component. Preferably, the hydrotalcite is used in conjunction withat least one cationic polymer. The term “cationic polymer”, as usedherein, refers to an organic polymer having one or more cationic groups,preferably an overall cationic charge. The cationic polymer may alsocontain anionic groups, and such polymers are commonly also referred toas amphoteric polymers.

Polymers suitable for use in the process can be derived from natural orsynthetic sources, and they can be linear, branched or cross-linked.Examples of suitable polymers include anionic, amphoteric and cationicpolysaccharides, preferably starches; anionic, amphoteric andchain-growth polymers, preferably cationic acrylamide-based polymers,including essentially linear, branched and cross-linked anionic andcationic acrylamide-based polymers; as well as cationicpoly(diallyldimethyl ammonium chloride); cationic polyethylene imines;cationic polyamines; cationic polyamideamines and vinylamide-basedpolymers, anionic step-growth polymers, preferably anionicnaphthalene-based condensation polymers. Cationic starch and cationicpolyacrylamide are particularly preferred polymers and they can be usedsingly, together with each other or together with other polymers, e.g.other cationic and/or anionic polymers. The molecular weight of thepolymer is suitably above 1,000,000 and preferably above 2,000,000. Theupper limit is not critical; it can be about 50,000,000, usually30,000,000 and suitably about 25,000,000. However, the molecular weightof polymers derived from natural sources may be higher.

Examples of suitable siliceous materials include anionic silica-basedparticles and anionic clays of the smectite type. Preferably, thesiliceous material has particles in the colloidal range of particlesize. Anionic silica-based particles, i.e. particles based on SiO₂ orsilicic acid, are preferably used and such particles are usuallysupplied in the form of aqueous colloidal dispersions, so-called sols.Examples of suitable silica-based particles include colloidal silica anddifferent types of polysilicic acid, either homopolymerised orco-polymerised. The silica-based sols can be modified and contain otherelements, e.g. aluminium, boron, nitrogen, zirconium, gallium, titatniumand the like, which can be present in the aqueous phase and/or in thesilica-based particles. Examples of suitable silica-based particles ofthis type include colloidal aluminium-modified silica and aluminiumsilicates. Mixtures of such suitable silica-based particles can also beused. Examples of suitable drainage and retention aids comprisinganionic silica-based particles include those disclosed in U.S. Pat. Nos.4,388,150; 4,927,498; 4,954,220; 4,961,825; 4,980,025; 5,127, 994;5,176, 891; 5,368,833; 5,447,604; 5,470,435; 5,543,014; 5,571,494;5,573,674; 5,584,966; 5,603,805; 5,688,482; and 5,707,493; which arehereby incorporated herein by reference.

Examples of suitable anionic silica-based particles include those havingan average particle size below about 100 nm, preferably below about 20nm and more preferably in the range of from about 1 to about 10 nm. Asconventional in the silica chemistry, the particle size refers to theaverage size of the primary particles, which may be aggregated ornon-aggregated. The specific surface area of the silica-based particlesis suitably above 50 m²/g and prefer-ably above 100 m² μg. Generally,the specific surface area can be up to about 1700 m²/g and preferably upto 1000 m²/g. The specific surface area is measured by means oftitration with NaOH in a well known manner, e.g. as described by G. W.Sears in Analytical Chemistry 28(1956): 12, 1981-1983 and in the U.S.Pat. No. 5,176,891. The given area thus represents the average specificsurface area of the particles.

Preferably, the anionic silica-based particles have specific surfacearea within the range of from 50 to 1000 m²/g, more preferably from 100to 950 m²/g. Sols of silica-based particles of these types alsoencompass modifications, for example with any of the elements mentionedabove. Preferably, the silica-based particles are present in a solhaving a S-value in the range of from 8 to 50%, preferably from 10 to40%, containing silica-based particles with a specific surface area inthe range of from 300 to 1000 m²/g, suitably from 500 to 950 m²/g, andpreferably from 750 to 950 m²/g, which sols can be modified as mentionedabove. The S-value can be measured and calculated as described by Iler &Dalton in J. Phys. Chem. 60(1956), 955-957. The S-value indicates thedegree of aggregation or microgel formation and a lower S-value isindicative of a higher degree of aggregation.

In yet another preferred embodiment of the invention, the silica-basedparticles are selected from polysilicic acid, either homopolymerised orco-polymerised, having a high specific surface area, suitably aboveabout 1000 m²/g. The specific surface area can be within the range offrom 1000 to 1700 m²/g and preferably from 1050 to 1600 m²/g. The solsof modified or co-polymerised polysilicic acid can contain otherelements as mentioned above. In the art, polysilicic acid is alsoreferred to as polymeric silicic acid, polysilicic acid microgel,polysilicate and polysilicate microgel, which all are encompassed by theterm polysilicic acid used herein. Aluminium-containing compounds ofthis type are commonly also referred to as polyaluminosilicate andpolyaluminosilicate microgel, which are both, encompassed by the termscolloidal aluminium-modified silica and aluminium silicate used herein.

Examples of suitable anionic clays of the smectite type includemontmorillonite/bentonite, hectorite, beidelite, nontronite, saponite,laponite, preferably bentonite. Examples of suitable anionic bentoniteclays include those disclosed in U.S. Pat. Nos. 4,753,710; 5,071,512;and 5,607,552, which are hereby incorporated herein by reference.

Examples of suitable cationic coagulants (also referred to as trashcatchers and fixatives) include water-soluble organic polymericcoagulants and inorganic coagulants. The cationic coagulants can be usedsingly or together, i.e. a polymeric coagulant can be used incombination with an inorganic coagulant. Examples of suitablewater-soluble organic polymeric cationic coagulants include cationicpolyamines, polyamideamines, polyethylene imines, dicyandiamidecondensation polymers and polymers of water soluble ethylenicallyunsaturated monomer or monomer blend which is formed of 50 to 100 mole %cationic monomer and 0 to 50 mole % other monomer. The amount ofcationic monomer is usually at least 80 mole %, suitably 100%. Examplesof suitable ethylenically unsaturated cationic monomers includedialkylaminoalkyl (meth)-acrylates and -acrylamides, preferably inquatemised form, and diallyl dialkyl ammonium chlorides, e.g. diallyldimethyl ammonium chloride (DADMAC), preferably homopolymers andcopolymers of DADMAC. The organic polymeric cationic coagulants usuallyhave a molecular weight in the range of from 1,000 to 700,000, suitablyfrom 10,000 to 500,000. Examples of suitable inorganic coagulantsinclude aluminium compounds, e.g. alum and polyaluminium compounds, e.g.polyaluminium chlorides, polyaluminium sulphates, polyaluminium silicatesulphates and mixtures thereof.

Examples of preferred drainage and retention systems according to theinvention comprise:

-   (i) anionic silica-based particles in combination with cationic    polysaccharides, preferably starch, or cationic chain-growth    polymers, preferably cationic acrylamide-based polymer, optionally    in combination with cationic coagulant;-   (ii) anionic silica-based particles in combination with anionic    acrylamide-based polymer, optionally in combination with cationic    organic polymer and/or cationic coagulant;-   (iii) bentonite in combination with cationic chain-growth polymers,    preferably cationic acrylamide-based polymer, optionally in    combination with cationic coagulant;-   (iv) cationic polysaccharide, preferably cationic starch, in    combination with anionic step-growth polymer, preferably anionic    naphthalene-based condensation polymer; optionally in combination    with cationic coagulant;-   (v) cationic chain-growth polymer, preferably cationic    acrylamide-based polymer, in combination with anionic step-growth    polymer, preferably anionic naphthalene-based condensation polymer,    optionally in combination with cationic coagulant;-   (vi) cationic chain-growth polymer, preferably cationic    acrylamide-based polymer, in combination with cationic coagulant;    and-   (vii) cationic chain-growth polymer, preferably cationic    acrylamide-based polymer, in combination with cross-linked anionic    and cationic acrylamide-based polymers.

The components of drainage and retention aids can be added to thecellulosic suspension in conventional manner and in any order. Whenusing a siliceous material, it is preferred to add a cationic polymer tothe suspension before adding the siliceous material, even if theopposite order of addition may also be used. It is further preferred toadd a cationic polymer before a shear stage, which can be selected frompumping, mixing, cleaning, etc., and to add the siliceous material afterthat shear stage. When using a cationic coagulant, it is preferablyintroduced into the suspension prior to introducing cationic polymer andsiliceous material, if used. Alternatively, the cationic coagulant andcationic polymer can be introduced into the suspension essentiallysimultaneously, either separately or in admixture, e.g. as disclosed inU.S. Pat. No. 5,858,174, which is hereby incorporated herein byreference.

If the hydrotalcite according to the invention is used together with adrainage and retention aid, the hydrotalcite can be added to thesuspension prior to or after the addition of the drainage and retentionaid. Preferably, the hydrotalcite is added prior to the addition ofdrainage and retention aid(s). Preferably, the hydrotalcite is added tothe thick stock, or to the thin stock, and the drainage and retentionaid is added to the thin stock. The hydrotalcite can also be added tothe re-cycled white water. If two or more drainage and retention aidsare used, i.e. a cationic polymer together with siliceous material, e.g.silica-based particles, and optionally anionic organic polymer, thehydrotalcite can be added to the cellulosic suspension (stock) prior to,after or in between the addition of the drainage and retention aids, ortogether with any of the drainage and retention aids. The hydrotalcitemay also be added at several locations in the process, e.g. to the thickstock and again to the thin stock prior to the addition of drainage andretention aid.

The drainage and retention aid(s) according to the invention can beadded to the stock to be dewatered in amounts which can vary within widelimits depending on, inter alia, type and number of components, type ofcellulosic suspension, salt content, type of salts, filler content, typeof filler, point of addition, degree of white water closure, etc.Generally, the retention and drainage aid(s) are added in amounts thatgive better drainage and/or retention than is obtained when not addingthe components. The cationic polymer is usually added in an amount of atleast about 0.001% by weight, often at least about 0.005% by weight,based on dry cellulosic suspension, and the upper limit is usually about3% and suitably about 1.5% by weight. Commonly applied addition amountsof cationic polymer are from about 0.01% up to about 0.5% by weight.Anionic materials, e.g. siliceous materials, i.e. anionic silica-basedparticles and anionic clays of the smectite type, and anionic organicpolymers, are usually added in an amount of at least about 0.001% byweight, often at least about 0.005% by weight, based on dry cellulosicsuspension, and the upper limit is usually about 1.0% and suitably about0.6% by weight.

When using a cationic coagulant in the process, it can be added in anamount of at least about 0.001% by weight, calculated as dry coagulanton dry cellulosic suspension. Suitably, the amount is in the range offrom about 0.05 up to about 3.0%, preferably in the range from about 0.1up to about 2.0%.

Furthermore, the process can also be useful in the manufacture of boardfrom cellulosic suspensions having high conductivity. In such cases, theconductivity of the suspension that is dewatered on the wire is usuallyat least 1.0 mS/cm, suitably at least 2.0 mS/cm, and preferably at least3.5 mS/cm. Conductivity can be measured by standard equipment such as,for example, a WTW LF 539 instrument supplied by Christian Berner. Thevalues referred to above are suitably determined by measuring theconductivity of the cellulosic suspension that is fed into or present inthe head box of the board machine or, alternatively, by measuring theconductivity of white water obtained by dewatering the suspension.

The present invention further encompasses board making processes wherewhite water is extensively recycled, or recirculated, i.e. with a highdegree of white water closure, for example where from 0 to 30 tons offresh water are used per ton of dry board produced, usually less than20, suitably less than 15, preferably less than 10 and notably less than5 tons of fresh water per ton of board.

The invention further relates to a method for producing a packagingmaterial which comprises providing board comprising one or more pliescontaining cellulosic fibres and hydrotalcite, as defined herein, andsubjecting the board to one or more converting operations selected fromprinting, varnishing, coating, e.g. plastics coating, extrusion coating,barrier coating, laminating, e.g. plastic film laminating and metal foillaminating, e.g aluminium foil laminating, metallizing, die cutting,i.e. stamping out blanks, creasing, scoring, stripping, i.e. removal ordebris, blanking, i.e. separation of blanks, foil blocking, embossingand folding. The term “creasing”, as used herein, is also referred to asscoring and grooving. Preferably, the method includes one or moreconverting operations comprising scoring or creasing, more preferablytwo or more operations comprising scoring or creasing, for examplecutting and scoring or creasing.

The invention also relates to a packaging material comprising boardwhich comprises one or more plies containing cellulosic fibres andhydrotalcite, as defined herein, wherein it further comprises one ormore creases. The creases, also referred to as scores, grooves orfolding lines, make it easier to fold and erect the packaging materialprior to filling. The packaging materials of the invention can have oneor more layers of plastic film, metal foil, e.g. aluminium, and/orbarrier coating.

The invention further relates to a procedure of making a package whichcomprises providing a blank of packaging material comprising boardcomprising one or more plies containing cellulosic fibres andhydrotalcite, as defined herein; filling the blank with a solid orliquid content to obtain an unsealed package; and then sealing theobtained package. Preferably the packaging material comprises one ormore grooves, creases or scores. The term “blank”, as used herein, meansan unfilled package or packaging material. Preferably the blank isfolded and erected prior to filling. Examples of suitable methods forsealing include gluing and heat sealing.

Examples of suitable solid and liquid contents include solid and liquidfoodstuffs, e.g. tomato products, soup and cream; beverages, e.g. milk,fruit juice, wine and water; pharmaceuticals; cosmetics; chocolates;cigarettes and tobacco. In a preferred embodiment, the invention furthercomprises sterilizing the package and/or the content. The term“sterilizing”, as used herein, means reducing the number ofmicroorganisms. Examples of suitable methods and means for sterilizationinclude heat, e.g. rapid heating and cooling, chemicals, e.g. hydrogenperoxide, irradiation, e.g. IR and UV irradiation. The filling can bemade under sterile conditions.

The invention also relates to a package comprising board comprising oneor more plies containing cellulosic fibres and hydrotalcite, as definedherein, wherein it further comprises a solid or liquid content. Theinvention further relates to uses of the packaging material comprisingboard, which comprises one or more plies containing cellulosic fibresand hydrotalcite, as defined herein, for packaging of solid or liquidfoodstuffs, beverages, pharmaceuticals, cosmetics, chocolates,cigarettes or tobacco.

Examples of suitable packaging of the invention include foodstuffpackaging, beverage packaging, sterile packaging and aseptic packaging.

The invention is further illustrated in the following example which,however, is not intended to limit the same. Parts and % relate to partsby weight and % by weight, respectively, unless otherwise stated.

EXAMPLE 1

In this example, the efficiency of the invention to reduce undesirableand/or unpleasant taste, smell and/or odour of board was evaluated.

A chemical substance which is present in board and causes undesirabletaste, smell and/or odour, n-hexanal, was chosen as a smelling modelsubstance, hereinafter “smelling substance”. The content of the smellingsubstance was determined by the so-called hot method in which a sampleconsisting of 2.5 g of packaging material was placed in a vessel whichthen was sealed. After shaking for 5 min and subsequent thermostating at100° C. for 40 min, an amount of gas above the sample was retrieved andimmediately analysed in a gas chromatograph. The content of the smellingsubstance in the amount of gas was calculated from the top area of thechromatogram. The degree of undesirable taste, smell and/or odour wasgiven as the smelling substance residue, which constitutes a percentageshare of the content of smelling substance transferred from thecellulosic sheet or pulp containing hydrotalcite in relation to thecorresponding content transferred from the sheet or pulp withoutadditives. Thus, the content of smelling substance transferred from thesheet or pulp without any addition of hydrotalcite or paper chemicalswas calculated.

Plies of board with and without hydrotalcite were produced on a pilotmachine. A thick cellulosic suspension (thick stock) was used based onfurnish from a liquid packaging board mill consisting of 30% bleachedsoftwood pulp and 70% bleached hardwood pulp. The thick suspension wasdiluted with press water from bleached hardwood pulp to provide aconsistency of 15 g/l. The obtained suspension had a pH of 7 andconductivity of 0.8 mS/cm. The suspension was stirred and heated to 50°C. In one test, 50 kg/t hydrotalcite (CC-22, Akzo Nobel Catalyst B.V.)was added to the suspension. The suspension was stirred for 30 minutes.

Prior to sheet formation, the following additives were added to thesuspension in the following order: 8% calcinated clay; 1 kg/t aluminiumsulfate; 4 kg/t cationic starch (Perlbond 970); 1.6 kg/t rosin-basedsizing agent (Eka Composize L44HT); 1.5 kg/t aluminium sulfate; 1.5 kg/tsizing agent based on alkenyl ketene dimer (Eka Keydime 28HF); 5 kg/tcationic starch (Perlbond 970); and 2.5 kg/t silica sol (Eka NP 442).The suspension was dewatered to form a sheet having a basis weight ofapproximately 90 g/m².

Directly after production, A4 sized sheets were wrapped in aluminiumfoil and sealed in air tight plastic bags. After two weeks, the sheetwas analysed with gas chromatography for the smelling substance. Table 1shows the amount of the smelling substance after storage for two weeks.TABLE 1 Hydrotalcite Smelling Substance Test No. [kg/t] [ng/ml] 1 0 1682 50 110

Example 1 shows that the invention resulted in a 35% reduction of thecontent of the volatile smelling substance in the gas phase.

EXAMPLE 2

Board was made as described in Example 1 except that the amount ofhydrotalcite added was different. The board obtained was analysed forfiller content, also referred to as ash retention. Table 2 shows theresults. TABLE 2 Hydrotalcite Test No. [kg/t] Filler [%] 1 0 7.6 2 108.2

Table 2 shows that the filler level was higher when adding hydrotalcitein the process.

EXAMPLE 3

In this example, sizing performance was evaluated. A cellulosicsuspension from a liquid packaging board mill was treated withhydrotalcite having the 3R₂ stacking (CC-22, Akzo Nobel Catalyst B. V.)and with talc (Finntalc P05, Omya) respectively. Sizing, drainage andretention aids were added and hand sheets were made (SCAN-C 26:76).Sizing of the sheets was measured as Cobb 60 values (SCAN-P 12:64).

A thick cellulosic suspension (thick stock) was used based on furnishfrom a liquid packaging board (LPB) mill consisting of bleached softwoodand hardwood pulp. The suspension was stirred and heated to 50° C.Hydrotalcite or talc was added to the suspension which was stirred for30 minutes. The thick suspension was then diluted with tap water to aconsistency of 5 g/L. The obtained suspension had a pH of 8 andconductivity of 0.7 mS/cm. Before sheet making, 0.3 kg/ton of dry pulpof AKD (Keydime C223, Eka Chemicals), 8 kg/ton of dry pulp of cationicstarch (Perlbond 970) and 0.5 kg/ton of dry pulp of silica-basedparticles (Eka NP 590, Eka Chemicals) were added. The sheets had a basisweight of approximately 73 g/m². Table 3 shows the sizing resultsobtained by addition of different amounts of talc and hydrotalcite tothe liquid packaging board furnish. TABLE 3 Test No. Talc [kg/t] CC-22[kg/t] Cobb 60 1 0 0 40 2 1 44 3 5 60 4 1 35 5 5 34

The sizing performance was improved when using hydrotalcite over talc.The cellulosic sheet containing bleached pulp and hydrotalcite can beused as a ply of single ply board and multi ply board, e.g. top and/orback ply.

EXAMPLE 4

Sizing performance was evaluated with higher additions of hydrotalcite(CC-22, Akzo Nobel Catalyst B.V.) and talc (Finntalc PO₅, Omya),respectively. Hand sheets were made and sizing performance was measuredas Cobb 60 (SCAN-P 12:64) values.

A thick cellulosic suspension was used based on furnish from a LPB millconsisting of hydrogen peroxide bleached softwood and hardwood sulphatepulp at −4% consistency. This suspension was stirred and heated to 50°C. Hydrotalcite or talc was added to the suspension which was allowed tostand for 20 minutes. The thick suspension was then diluted with bleachfiltrate to ˜3.9 g/l consistency. To the furnish AKD, 1.6 kg/t rosinsize, 1.6 kg/t alum, 5.0 kg/t cationic starch and 0.35 kg/t silica-basedparticles (Eka NP 590, Eka Chemicals) were added before making handsheets (Rapid-Köthen former). The sheets had a basis weight ofapproximately 100 g/m². Table 4 summarized the sizing results obtainedby sizing the liquid packaging board furnish. TABLE 4 Test No. AKD[kg/t] Talc [kg/t] CC-22 [kg/t] COBB 60 1 0 0 0 258 2 0.5 0 0 250 3 0.80 0 131 4 1 0 0 59 5 1.4 0 0 39 6 0.5 5 0 211 7 0.8 5 0 115 8 1 5 0 61 91.4 5 0 39 10 0.5 0 10 198 11 0.8 0 10 87 12 1 0 10 45 13 1.4 0 10 33

Table 4 shows that the sizing performance was improved (lower Cobb 60values) using hydrotalcite compared to talc. The cellulosic sheetcontaining bleached pulp and hydrotalcite can be used as a ply of singleply board and multi ply board, e.g. top and/or back ply.

EXAMPLE 5

This example was made in a de-inked pulp (DIP) mill. An aqueous pulpsuspension from the DIP mill was treated with hydrotalcite (CC-22, AkzoNobel Catalyst B.V.). The turbidity of the pulp filtrate was thenmeasured.

The pulp suspension used was a taken between the disc filter and thescrew press in the DIP plant. The pulp suspension had a consistency of˜7%, and was diluted with tap water to ˜4.2%. This suspension pulp wasstirred and heated at 50° C. The hydrotalcite was added to the pulpsuspension which was allowed to stand for 30 minutes. The pulpsuspension was then filtrated through a GF/A glass fibre filter (˜2 μmhole diameters). The filtrate was analysed for turbidity in a Hach 2100Pturbidity meter. Table 5 shows the results. TABLE 5 Test No. CC-22[kg/t] Turbidity [NTU] 1 0 71.8 2 2 63.5 3 5 42.3

The turbidity of the filtrate improved (decreased) when mixing de-inkedpulp with hydrotalcite before filtering. A cellulosic sheet containingDIP and hydrotalcite can be used as a ply of multi ply board, e.g.undertop and/or middle ply.

1. A process for producing board which comprises (i) providing anaqueous suspension comprising cellulosic fibres; (ii) addinghydrotalcite to the suspension; (iii) dewatering the obtained suspensionto provide a single ply board.
 2. The process of claim 1, furthercomprising attaching said ply to one or more plies comprising cellulosicfibres to provide a multi ply board comprising two or more plies.
 3. Theprocess of claim 1, further comprising adding a cationic polymer to thesuspension.
 4. The process of claim 1, further comprising adding asiliceous material to the suspension.
 5. The process of claim 1, furthercomprising adding a sizing agent to the suspension.
 6. The process ofclaim 1, wherein the hydrotalcite has a 3R₁ stacking.
 7. The process ofclaim 1, wherein the hydrotalcite has a 3R₂ stacking.
 8. The process ofclaim 2, wherein the hydrotalcite has a 3R₂ stacking.
 9. A boardcomprising one or more plies containing cellulosic fibres, wherein theboard further comprises hydrotalcite distributed throughout at least oneof said one or more plies.
 10. The board of claim 9, wherein the boardcomprises two or more plies containing cellulosic fibres.
 11. The boardof claim 10, wherein the board comprises from three to seven pliescontaining cellulosic fibres.
 12. The board of claim 11, whereinhydrotalcite is comprised in at least one outer ply of the board. 13.The board of claim 9, wherein the hydrotalcite has a 3R₁ stacking. 14.The board of claim 9, wherein the hydrotalcite has a 3R₂ stacking. 15.The board of claim 10, wherein the hydrotalcite has a 3R₂ stacking. 16.The board of claim 9, wherein the board has a grammage of at least 130g/m².
 17. The board of claim 9, wherein the board has a grammage of from150 to 450 g/m².
 18. The board of claim 9, wherein the board has a bulkdensity of 200 to 600 kg/m³.
 19. The board of claim 9, wherein thehydrotalcite is substantially uniformly distributed throughout at leastone ply of the board.
 20. The board of claim 9, wherein the boardcomprises at least 50% by weight of cellulosic fibres.